Methods and systems for redox flow battery electrolyte hydration

ABSTRACT

Methods and systems are provided for transporting and hydrating a redox flow battery system with a portable field hydration system. In one example, the redox flow battery system may be hydrated with the portable field hydration system in a dry state, in the absence of liquids. In this way, a redox flow battery system may be assembled and transported from a battery manufacturing facility to an end-use location off-site while the redox flow battery system is in the dry state, thereby reducing shipping costs, design complexities, as well as logistical and environmental concerns.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Non-Provisionalapplication Ser. No. 15/965,671, entitled “METHODS AND SYSTEMS FOR REDOXFLOW BATTERY ELECTROLYTE HYDRATION,” filed on Apr. 27, 2018. ApplicationSer. No. 15/965,671 claims priority to U.S. Provisional Application No.62/491,970, entitled “METHODS AND SYSTEMS FOR REDOX FLOW BATTERYELECTROLYTE HYDRATION”, and filed on Apr. 28, 2017. The entire contentsof the above-listed applications are hereby incorporated by referencefor all purposes.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with government support under contract no.DEAR0000261 awarded by the DOE, Office of ARPA-E. The government hascertain rights in the invention.

FIELD

The present description relates generally to electrolyte preparation fora redox flow battery system.

BACKGROUND AND SUMMARY

Redox flow batteries are suitable for grid scale storage applicationsdue to their capabilities of scaling power and capacity independently,and charging and discharging for thousands of cycles with minimalperformance losses. Electrolyte, including aqueous solutions comprisingwater and salts and/or acids, are recirculated between electrolyte tanksand the redox flow battery cells in order to supply sufficientelectrolyte to carry of the redox reactions for battery charging anddischarging. Commissioning a new redox flow battery system traditionallyinvolves hydrating and filling a redox flow battery system, includingthe electrolyte tanks, at a battery vendor's manufacturing facility,prior to transporting the redox flow battery system to and installingthe redox flow battery system at the end-use location.

The inventors herein have recognized potential issues with the abovemethods. Namely, a filled and hydrated redox flow battery system isheavy and cumbersome, and transport of filled and hydrated redox flowbattery systems can be difficult and expensive. Furthermore,transporting of redox flow battery systems between a batteryvendor/manufacturing facility and an end-use site may involve variousmodes of transportation such as by truck, by rail, and by ship overlarge distances, which may be slower when the redox flow battery systemis filled and hydrated. In addition, the overall system may be modifiedto accommodate transporting a large quantity of mixed and hydratedchemicals to be structurally sound across various modes oftransportation.

In one example, the issues described above may be addressed by a methodof operating a redox flow battery system, the redox flow battery systemincluding first and second electrolyte chambers fluidly coupled to aredox flow battery cell, the method comprising: during a firstcondition, including when the redox flow battery system is in a drystate without water and liquid solvents, adding first and second amountsof dry electrolyte precursor to the first and second electrolytechambers, respectively, the first and second amounts corresponding to adesired concentration of first and second electrolytes in the first andsecond electrolyte chambers during an operating mode, including when theredox flow battery system is being charged or discharged, fluidlycoupling the redox flow battery system to a field hydration system, thefield hydration system including a water supply pump fluidly coupled toa water source, and supplying water from the field hydration system tothe redox flow battery system, wherein the redox flow battery systemwould remain in the dry state without the water from the field hydrationsystem.

In this way, a redox flow battery system may be assembled andtransported from a battery manufacturing facility to an end-use locationoff-site while the redox flow battery system is in a dry state, therebyreducing shipping costs, design complexities, environmental concerns,and the amount of time to prepare a customer-ready redox flow batterysystem. Furthermore the methods and system herein facilitatecommissioning of the redox flow battery system, including hydration ofthe redox flow battery system in the dry state, that can be performed bya 3rd party or customer utilizing a field hydration system at theend-use location remotely from the battery manufacturing facility. Inthis manner, the customer can more flexibly and independently schedulethe commissioning of the redox flow battery system, which can increasecustomer satisfaction and reduce operation logistics complexities. Insome examples, the methods and systems herein further facilitatecommissioning of the redox flow battery system, including on-sitehydration by a customer, followed by draining of the redox flow batterysystem, and shipment to a second in-use location where it can berehydrated for energy storage applications at the second in-uselocation.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic of an example redox flow battery system.

FIG. 2 shows a schematic of an example field hydration system.

FIG. 3 shows a high-level flow chart for a method of hydrating a redoxflow battery system with the field hydration system of FIG. 2 .

FIGS. 4A, 4B, and 4C show flow charts for a method for hydrating a redoxflow battery system with the field hydration system of FIG. 2 .

DETAILED DESCRIPTION

The following description relates to systems and methods for flowingwater to electrolytes configured to store electrical energy for a redoxflow battery. The redox flow battery is shown in FIG. 1 includes anintegrated multi-chamber storage tank having separate positive andnegative electrolyte chambers. Prior to installation and commissioningof the redox flow battery system, the redox flow battery system may beassembled and delivered to a desired end-use location, different from alocation where the battery was assembled, with dry electrolyte stored inthe positive and negative electrolyte chambers. The dry electrolyteincludes electrolyte granules or precursors free of liquid water and/orother liquid solvents in a moisture free state. Once delivered to theend-use location, the assembled redox flow battery system may beinstalled thereat, thereby fixing a position of the redox flow batterysystem. A field hydration system, shown in FIG. 2 , may be delivered tothe end-use location along with the assembled redox flow battery system,and coupled between a water source at the desired end-use location andthe installed redox flow battery system. The field hydration system ofFIG. 2 can facilitate staged hydration, filling, and preparation of theredox flow battery system, by way of methods illustrated in FIGS. 3 and4A-4C.

FIGS. 1-2 show example configurations with relative positioning of thevarious components. If shown directly contacting each other, or directlycoupled, then such elements may be referred to as directly contacting ordirectly coupled, respectively, at least in one example. Similarly,elements shown contiguous or adjacent to one another may be contiguousor adjacent to each other, respectively, at least in one example. As anexample, components laying in face-sharing contact with each other maybe referred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example. Asyet another example, elements shown above/below one another, at oppositesides to one another, or to the left/right of one another may bereferred to as such, relative to one another. Further, as shown in thefigures, a topmost element or point of element may be referred to as a“top” of the component and a bottommost element or point of the elementmay be referred to as a “bottom” of the component, in at least oneexample. As used herein, top/bottom, upper/lower, above/below, may berelative to a vertical axis of the figures and used to describepositioning of elements of the figures relative to one another. As such,elements shown above other elements are positioned vertically above theother elements, in one example. As yet another example, shapes of theelements depicted within the figures may be referred to as having thoseshapes (e.g., such as being circular, straight, planar, curved, rounded,chamfered, angled, or the like). Further, elements shown intersectingone another may be referred to as intersecting elements or intersectingone another, in at least one example. Further still, an element shownwithin another element or shown outside of another element may bereferred as such, in one example. It will be appreciated that one ormore components referred to as being “substantially similar and/oridentical” differ from one another according to manufacturing tolerances(e.g., within 1-5% deviation).

Hybrid redox flow batteries are redox flow batteries that arecharacterized by the deposit of one or more of the electro-activematerials as a solid layer on an electrode. Hybrid redox flow batteriesmay, for instance, include a chemical that plates via an electrochemicalreaction as a solid on a substrate throughout the battery chargeprocess. During battery discharge, the plated species may ionize via anelectrochemical reaction, becoming soluble in the electrolyte. In hybridbattery systems, the charge capacity (e.g., amount of energy stored) ofthe redox battery may be limited by the amount of metal plated duringbattery charge and may accordingly depend on the efficiency of theplating system as well as the available volume and surface areaavailable for plating.

In a redox flow battery system the negative electrode 26 may be referredto as the plating electrode and the positive electrode 28 may bereferred to as the redox electrode. The negative electrolyte within theplating side (e.g., negative electrode compartment 20) of the batterymay be referred to as the plating electrolyte and the positiveelectrolyte on the redox side (e.g. positive electrode compartment 22)of the battery may be referred to as the redox electrolyte.

Anode refers to the electrode where electro-active material loseselectrons and cathode refers to the electrode where electro-activematerial gains electrons. During battery charge, the positiveelectrolyte gains electrons at the negative electrode 26; therefore thenegative electrode 26 is the cathode of the electrochemical reaction.During discharge, the positive electrolyte loses electrons; thereforethe negative electrode 26 is the anode of the reaction. Accordingly,during charge, the negative electrolyte and negative electrode may berespectively referred to as the catholyte and cathode of theelectrochemical reaction, while the positive electrolyte and thepositive electrode may be respectively referred to as the anolyte andanode of the electrochemical reaction. Alternatively, during discharge,the negative electrolyte and negative electrode may be respectivelyreferred to as the anolyte and anode of the electrochemical reaction,while the positive electrolyte and the positive electrode may berespectively referred to as the catholyte and cathode of theelectrochemical reaction. For simplicity, the terms positive andnegative are used herein to refer to the electrodes, electrolytes, andelectrode compartments in redox battery flow systems.

One example of a hybrid redox flow battery is an all iron redox flowbattery (IFB), in which the electrolyte comprises iron ions in the formof iron salts (e.g., FeCl₂, FeCl₃, and the like), wherein the negativeelectrode comprises metal iron. For example, at the negative electrode,ferrous ion, Fe²⁺, receives two electrons and plates as iron metal on tothe negative electrode 26 during battery charge, and iron metal, Fe⁰,loses two electrons and re-dissolves as Fe²⁺ during battery discharge.At the positive electrode, Fe²⁺ loses an electron to form ferric ion,Fe³⁺, during charge, and during discharge Fe³⁺ gains an electron to formFe²⁺. The electrochemical reaction is summarized in equations (1) and(2), wherein the forward reactions (left to right) indicateelectrochemical reactions during battery charge, while the reversereactions (right to left) indicate electrochemical reactions duringbattery discharge:

Fe²⁺+2e−↔Fe⁰−0.44 V (Negative Electrode)  (1)

2Fe²⁺↔2 Fe³⁺+2e−+0.77 V (Positive Electrode)  (2)

As discussed above, the negative electrolyte used in the all iron redoxflow battery (IFB) may provide a sufficient amount of Fe²⁺ so that,during charge, Fe²⁺ can accept two electrons from the negative electrodeto form Fe⁰ and plate onto a substrate. During discharge, the plated Fe⁰may then lose two electrons, ionizing into Fe²⁺ and be dissolved backinto the electrolyte. The equilibrium potential of the above reaction is−0.44V and thus this reaction provides a negative terminal for thedesired system. On the positive side of the IFB, the electrolyte mayprovide Fe²⁺ during charge which loses electron and oxidizes to Fe³⁺.During discharge, Fe³⁺ provided by the electrolyte becomes Fe²⁺ byabsorbing an electron provided by the electrode. The equilibriumpotential of this reaction is +0.77V, creating a positive terminal forthe desired system.

The IFB provides the ability to charge and recharge its electrolytes incontrast to other battery types utilizing non-regenerating electrolytes.Charge is achieved by applying a current across the electrodes viaterminals 40 and 42. The negative electrode may be coupled via terminal40 to the negative side of a voltage source so that electrons may bedelivered to the negative electrolyte via the positive electrode (e.g.,as Fe²⁺ is oxidized to Fe³⁺ in the positive electrolyte in the positiveelectrode compartment 22). The electrons provided to the negativeelectrode 26 (e.g., plating electrode) can reduce the Fe²⁺ in thenegative electrolyte to form Fe⁰ at the plating substrate causing it toplate onto the negative electrode.

Discharge can be sustained while Fe⁰ remains available to the negativeelectrolyte for oxidation and while Fe³⁺ remains available in thepositive electrolyte for reduction. As an example, Fe³⁺ availability canbe maintained by increasing the concentration or the volume of thepositive electrolyte to the positive electrode compartment 22 side ofcell 18 to provide additional Fe³⁺ ions via an external source, such asan external positive electrolyte tank 52. More commonly, availability ofFe⁰ during discharge may be an issue in IFB systems, wherein the Fe⁰available for discharge may be proportional to the surface area andvolume of the negative electrode substrate as well as the platingefficiency. Charge capacity may be dependent on the availability of Fe²⁺in the negative electrode compartment 20. As an example, Fe²⁺availability can be maintained by providing additional Fe²⁺ ions via anexternal source, such as an external negative electrolyte tank 50 toincrease the concentration or the volume of the negative electrolyte tothe negative electrode compartment 20 side of cell 18.

In an IFB, the positive electrolyte comprises ferrous ion, ferric ion,ferric complexes, or any combination thereof, while the negativeelectrolyte comprises ferrous ion or ferrous complexes, depending on thestate of charge of the IFB system. As previously mentioned, utilizationof iron ions in both the negative electrolyte and the positiveelectrolyte allows for utilization of the same electrolytic species onboth sides of the battery cell, which can reduce electrolytecross-contamination and can increase the efficiency of the IFB system,resulting in less electrolyte replacement as compared to other redoxflow battery systems.

Efficiency losses in an IFB may result from electrolyte crossoverthrough the separator 24 (e.g., ion-exchange membrane barrier,micro-porous membrane, and the like). For example, ferric ions in thepositive electrolyte may be driven toward the negative electrolyte by aferric ion concentration gradient and an electrophoretic force acrossthe separator. Subsequently, ferric ions penetrating the membranebarrier and crossing over to the negative electrode compartment 20 mayresult in coulombic efficiency losses. Ferric ions crossing over fromthe low pH redox side (e.g., more acidic positive electrode compartment22) to high pH plating side (e.g., less acidic negative electrodecompartment 20) can result in precipitation of Fe(OH)₃. Precipitation ofFe(OH)₃ can damage the separator 24 and cause permanent batteryperformance and efficiency losses. For example, Fe(OH)₃ precipitate maychemically foul the organic functional group of an ion-exchange membraneor physically clog the small micro-pores of an ion-exchange membrane. Ineither case, due to the Fe(OH)₃ precipitate, membrane ohmic resistancemay rise over time and battery performance may degrade. Precipitate maybe removed by washing the battery with acid, but the constantmaintenance and downtime may be disadvantageous for commercial batteryapplications. Furthermore, washing may be dependent on regularpreparation of electrolyte, an adding to process cost and complexity.Adding specific organic acids to the positive electrolyte and thenegative electrolyte in response to electrolyte pH changes may alsomitigate precipitate formation during battery charge and dischargecycling.

Additional coulombic efficiency losses may be caused by reduction of H⁺(e.g., protons) and subsequent formation of H₂ (e.g., hydrogen gas), andthe reaction of protons in the negative electrode compartment 20 withelectrons supplied at the plated iron metal electrode to form hydrogengas.

The IFB electrolyte (e.g., FeCl₂, FeCl₃, FeSO₄, Fe₂(SO₄)₃, and the like)is readily available and can be produced at low costs. The IFBelectrolyte offers higher reclamation value because the same electrolytecan be used for the negative electrolyte and the positive electrolyte,consequently reducing cross contamination issues as compared to othersystems. Furthermore, owing to its electron configuration, iron maysolidify into a generally uniform solid structure during plating thereofon the negative electrode substrate. For zinc and other metals commonlyused in hybrid redox batteries, solid dendritic structures may formduring plating. The stable electrode morphology of the IFB system mayincrease the efficiency of the battery in comparison to other redox flowbatteries. Further still, iron redox flow batteries reduce the use oftoxic raw materials and can operate at a relatively neutral pH ascompared to other redox flow battery electrolytes. Accordingly, IFBsystems reduce environmental hazards as compared with all other currentadvanced redox flow battery systems in production.

FIG. 1 provides a schematic illustration of a redox flow battery system10. The redox flow battery system 10 may comprise a redox flow batterycell 18 fluidly connected to a multi-chambered electrolyte storage tank110. The redox flow battery cell 18 may generally include a negativeelectrode compartment 20, separator 24, and positive electrodecompartment 22. The separator 24 may comprise an electrically insulatingionic conducting barrier which prevents bulk mixing of the positiveelectrolyte and the negative electrolyte while allowing conductance ofspecific ions therethrough. For example, the separator 24 may comprisean ion-exchange membrane and/or a microporous membrane. The negativeelectrode compartment 20 may comprise a negative electrode 26, and anegative electrolyte comprising electroactive materials. The positiveelectrode compartment 22 may comprise a positive electrode 28, and apositive electrolyte comprising electroactive materials. In someexamples, multiple redox flow battery cells 18 may be combined in seriesor parallel to generate a higher voltage or current in a redox flowbattery system. Further illustrated in FIG. 1 are negative and positiveelectrolyte pumps 30 and 32, both used to pump electrolyte solutionthrough the flow battery system 10. Electrolytes are stored in one ormore tanks external to the cell, and are pumped via negative andpositive electrolyte pumps 30 and 32 through the negative electrodecompartment 20 side and the positive electrode compartment 22 side ofthe battery, respectively.

As illustrated in FIG. 1 , the redox flow battery cell 18 may furtherinclude negative battery terminal 40, and positive battery terminal 42.When a charge current is applied to the battery terminals 40 and 42, thepositive electrolyte is oxidized (lose one or more electrons) at thepositive electrode 28, and the negative electrolyte is reduced (gain oneor more electrons) at the negative electrode 26. During batterydischarge, reverse redox reactions occur on the electrodes. In otherwords, the positive electrolyte is reduced (gain one or more electrons)at the positive electrode 28, and the negative electrolyte is oxidized(lose one or more electrons) at the negative electrode 26. Theelectrical potential difference across the battery is maintained by theelectrochemical redox reactions in the positive electrode compartment 22and the negative electrode compartment 20, and can induce a currentthrough a conductor while the reactions are sustained. The amount ofenergy stored by a redox battery is limited by the amount ofelectro-active material available in electrolytes for discharge,depending on the total volume of electrolytes and the solubility of theelectro-active materials.

The flow battery system 10 may further comprise an integratedmulti-chambered electrolyte storage tank 110. The multi-chamberedstorage tank 110 may be divided by a bulkhead 98. The bulkhead 98 maycreate multiple chambers within the storage tank so that both thepositive and negative electrolyte may be included within a single tank.The negative electrolyte chamber 50 holds negative electrolytecomprising electroactive materials, and the positive electrolyte chamber52 holds positive electrolyte comprising electroactive materials. Thebulkhead 98 may be positioned within the multi-chambered storage tank110 to yield a desired volume ratio between the negative electrolytechamber 50 and the positive electrolyte chamber 52. In one example, thebulkhead 98 may be positioned to set the volume ratio of the negativeand positive electrolyte chambers according to the stoichiometric ratiobetween the negative and positive redox reactions. The figure furtherillustrates the fill height 112 of storage tank 110, which may indicatethe liquid level in each tank compartment. The figure also shows gashead space 90 located above the fill height 112 of negative electrolytechamber 50, and gas head space 92 located above the fill height 112 ofpositive electrolyte chamber 52. The gas head space 92 may be utilizedto store hydrogen gas generated through operation of the redox flowbattery (e.g., due to proton reduction and corrosion side reactions) andconveyed to the multi-chambered storage tank 110 with returningelectrolyte from the redox flow battery cell 18. The hydrogen gas may beseparated spontaneously at the gas-liquid interface (e.g., fill height112) within the multi-chambered storage tank 110, thereby precludinghaving additional gas-liquid separators as part of the redox flowbattery system. Once separated from the electrolyte, the hydrogen gasmay fill the gas head spaces 90 and 92. A such, the stored hydrogen gascan aid in purging other gases from the multi-chamber storage tank 100,thereby acting as an inert gas blanket for reducing oxidation ofelectrolyte species, which can help to reduce redox flow batterycapacity losses. In this way, utilizing the integrated multi-chamberedstorage tank 110 may forego having separate negative and positiveelectrolyte storage tanks, hydrogen storage tanks, and gas-liquidseparators common to conventional redox flow battery systems, therebysimplifying the system design, reducing the physical footprint of thesystem, and reducing system costs.

FIG. 1 also shows the spill over-hole 96, which creates an opening inthe bulkhead 98 between gas head spaces 90 and 92, and provides a meansof equalizing gas pressure between the two chambers. The spill over hole96 may be positioned a threshold height above the fill height 112. Thespill over hole further enables a capability to self-balance theelectrolytes in each of the positive and negative electrolyte chambersin the event of a battery crossover. In the case of an all iron redoxflow battery system, the same electrolyte (Fe′) is used in both negativeand positive electrode compartments 20 and 22, so spilling over ofelectrolyte between the negative and positive electrolyte chambers 50and 52 may reduce overall system efficiency, but the overall electrolytecomposition, battery module performance, and battery module capacity aremaintained. Flange fittings may be utilized for all piping connectionsfor inlets and outlets to and from the multi-chambered storage tank 110to maintain a continuously pressurized state without leaks. Themulti-chambered storage tank can include at least one outlet from eachof the negative and positive electrolyte chambers, and at least oneinlet to each of the negative and positive electrolyte chambers.Furthermore, one or more outlet connections may be provided from the gashead spaces 90 and 92 for directing hydrogen gas to rebalancing reactors80 and 82.

Although not shown in FIG. 1 , integrated multi-chambered electrolytestorage tank 110 may further include one or more heaters thermallycoupled to each of the negative electrolyte chamber 50 and the positiveelectrolyte chamber 52. In alternate examples, only one of the negativeand positive electrolyte chambers may include one or more heaters. Inthe case where only the positive electrolyte chamber includes one ormore heaters, the negative electrolyte may be heated by transferringheat generated at the battery cells of the power module to the negativeelectrolyte. In this way, the battery cells of the power module may heatand facilitate temperature regulation of the negative electrolyte. Theone or more heaters may be actuated by the controller 88 to regulate atemperature of the negative electrolyte chamber 50 and the positiveelectrolyte chamber independently or together. For example, in responseto an electrolyte temperature decreasing below a threshold temperature,the controller may increase a power supplied to one or more heaters sothat a heat flux to the electrolyte is increased. The electrolytetemperature may be indicated by one or more temperature sensors mountedat the multi-chambered electrolyte storage tank 110, including sensors60 and 62. As examples the one or more heaters may include coil typeheaters or other immersion heaters immersed in the electrolyte fluid, orsurface mantle type heaters that transfer heat conductively through thewalls of the negative and positive electrolyte chambers to heat thefluid therein. Other known types of tank heaters may be employed withoutdeparting from the scope of the present disclosure. Furthermore,controller 88 may deactivate one or more heaters in the negative andpositive electrolyte chambers in response to a liquid level decreasingbelow a solids fill threshold level. Said in another way, controller 88may activate the one or more heaters in the negative and positiveelectrolyte chambers only in response to a liquid level increasing abovethe solids fill threshold level. In this way, activating the one or moreheaters without sufficient liquid in the positive and/or negativeelectrolyte chambers can be averted, thereby reducing a risk ofoverheating or burning out the heaters.

Further still, one or more inlet connections may be provided to each ofthe negative and positive electrolyte chambers from a field hydrationsystem 310. In this way, the field hydration system can facilitatecommissioning of the redox flow battery system, including installing,filling, and hydrating the system, at an end-use location. Furthermore,prior to its commissioning at the end-use location, the redox flowbattery system may be dry-assembled at a battery manufacturing facilitydifferent from end-use location without filling and hydrating thesystem, before delivering the system to the end-use location. In oneexample, the end-use location may correspond to the location where theredox flow battery system is to be installed and utilized for on-siteenergy storage. Said in another way, it is anticipated that, onceinstalled and hydrated at the end-use location, a position of the redoxflow battery system becomes fixed, and the redox flow battery system isno longer deemed a portable, dry system. Thus, from the perspective of aredox flow battery system end-user, the dry portable redox flow batterysystem may be delivered on-site, after which the redox flow batterysystem is installed, hydrated and commissioned. Prior to hydration theredox flow battery system may be referred to as a dry, portable system,the redox flow battery system being free of or without water and wetelectrolyte. Once hydrated, the redox flow battery system may bereferred to as a wet non-portable system, the redox flow battery systemincluding wet electrolyte.

Further illustrated in FIG. 1 , electrolyte solutions typically storedin the multi-chambered storage tank 110 are pumped via negative andpositive electrolyte pumps 30 and 32 throughout the flow battery system10. Electrolyte stored in negative electrolyte chamber 50 is pumped vianegative electrolyte pump 30 through the negative electrode compartment20 side, and electrolyte stored in positive electrolyte chamber 52 ispumped via positive electrolyte pump 32 through the positive electrodecompartment 22 side of the battery.

Two electrolyte rebalancing reactors 80 and 82, may be connected in-lineor in parallel with the recirculating flow paths of the electrolyte atthe negative and positive sides of the battery, respectively, in theredox flow battery system 10. One or more rebalancing reactors may beconnected in-line with the recirculating flow paths of the electrolyteat the negative and positive sides of the battery, and other rebalancingreactors may be connected in parallel, for redundancy (e.g., arebalancing reactor may be serviced without disrupting battery andrebalancing operations) and for increased rebalancing capacity. In oneexample, the electrolyte rebalancing reactors 80 and 82 may be placed inthe return flow path from the positive and negative electrodecompartments 20 and 22 to the positive and negative electrolyte chambers50 and 52, respectively. Electrolyte rebalancing reactors 80 and 82 mayserve to rebalance electrolyte charge imbalances in the redox flowbattery system occurring due to side reactions, ion crossover, and thelike, as described herein. In one example, electrolyte rebalancingreactors 80 and 82 may include trickle bed reactors, where the hydrogengas and electrolyte are contacted at catalyst surfaces in a packed bedfor carrying out the electrolyte rebalancing reaction. In other examplesthe rebalancing reactors 80 and 82 may include flow-through typereactors that are capable of contacting the hydrogen gas and theelectrolyte liquid and carrying out the rebalancing reactions in theabsence a packed catalyst bed.

During operation of a redox flow battery system, sensors and probes maymonitor and control chemical properties of the electrolyte such aselectrolyte pH, concentration, state of charge, and the like. Forexample, as illustrated in FIG. 1 , sensors 62 and 60 maybe bepositioned to monitor positive electrolyte and negative electrolyteconditions at the positive electrolyte chamber 52 and the negativeelectrolyte chamber 50, respectively. In another example, sensors 62 and60 may each include one or more electrolyte level sensors to indicate alevel of electrolyte in the positive electrolyte chamber 52 and thenegative electrolyte chamber 50, respectively, as described further withreference to FIG. 2 . As another example, sensors 72 and 70, alsoillustrated in FIG. 1 , may monitor positive electrolyte and negativeelectrolyte conditions at the positive electrode compartment 22 and thenegative electrode compartment 20, respectively. Sensors may bepositioned at other locations throughout the redox flow battery systemto monitor electrolyte chemical properties and other properties. Forexample a sensor may be positioned in an external acid tank (not shown)to monitor acid volume or pH of the external acid tank, wherein acidfrom the external acid tank is supplied via an external pump (not shown)to the redox flow battery system in order to reduce precipitateformation in the electrolytes. Additional external tanks and sensors maybe installed for supplying other additives to the redox flow batterysystem 10. For example, various sensors including, temperature,conductivity, and level sensors of a field hydration system 310 maytransmit signals to the controller 88. Furthermore, controller 88 maysend signals to actuators such as valves and pumps of the fieldhydration system 310 during hydration of the redox flow battery system.Sensor information may be transmitted to a controller 88 which may inturn actuate pumps 30 and 32 to control electrolyte flow through thecell 18, or to perform other control functions, as an example. In thismanner, the controller 88 may be responsive to, one or a combination ofsensors and probes.

Redox flow battery system 10 may further comprise a source of hydrogengas. In one example the source of hydrogen gas may comprise a separatededicated hydrogen gas storage tank. In the example of FIG. 1 , hydrogengas may be stored in and supplied from the integrated multi-chamberedelectrolyte storage tank 110. Integrated multi-chambered electrolytestorage tank 110 may supply additional hydrogen gas to the positiveelectrolyte chamber 52 and the negative electrolyte chamber 50.Integrated multi-chambered electrolyte storage tank 110 may alternatelysupply additional hydrogen gas to the inlet of electrolyte rebalancingreactors 80 and 82. As an example, a mass flow meter or other flowcontrolling device (which may be controlled by controller 88) mayregulate the flow of the hydrogen gas from integrated multi-chamberedelectrolyte storage tank 110. The integrated multi-chambered electrolytestorage tank 110 may supplement the hydrogen gas generated in redox flowbattery system 10. For example, when gas leaks are detected in redoxflow battery system 10 or when the reduction reaction rate is too low atlow hydrogen partial pressure, hydrogen gas may be supplied from theintegrated multi-chambered electrolyte storage tank 110 in order torebalance the state of charge of the electro-active species in thepositive electrolyte and negative electrolyte. As an example, controller88 may supply hydrogen gas from integrated multi-chambered electrolytestorage tank 110 in response to a measured change in pH or in responseto a measured change in state of charge of an electrolyte or anelectro-active species. For example an increase in pH of the negativeelectrolyte chamber 50, or the negative electrode compartment 20, mayindicate that hydrogen is leaking from the redox flow battery system 10and/or that the reaction rate is too slow with the available hydrogenpartial pressure, and controller 88, in response to the pH increase, mayincrease a supply of hydrogen gas from integrated multi-chamberedelectrolyte storage tank 110 to the redox flow battery system 10. As afurther example, controller 88 may supply hydrogen gas from integratedmulti-chambered electrolyte storage tank 110 in response to a pH change,wherein the pH increases beyond a first threshold pH or decreases beyondsecond threshold pH. In the case of an IFB, controller 88 may supplyadditional hydrogen to increase the rate of reduction of ferric ions andthe rate of production of protons, thereby reducing the pH of thepositive electrolyte. Furthermore, the negative electrolyte pH may belowered by hydrogen reduction of ferric ions crossing over from thepositive electrolyte to the negative electrolyte or by proton generatedat the positive side crossing over to the negative electrolyte due to aproton concentration gradient and electrophoretic forces. In thismanner, the pH of the negative electrolyte may be maintained within astable region, while reducing the risk of precipitation of ferric ions(crossing over from the positive electrode compartment) as Fe(OH)₃.Other control schemes for controlling the supply rate of hydrogen gasfrom integrated multi-chambered electrolyte storage tank 110 responsiveto a change in an electrolyte pH or to a change in an electrolyte stateof charge, detected by other sensors such as an oxygen-reductionpotential (ORP) meter or an optical sensor, may be implemented. Furtherstill, the change in pH or state of charge triggering the action ofcontroller 88 may be based on a rate of change or a change measured overa time period. The time period for the rate of change may bepredetermined or adjusted based on the time constants for the redox flowbattery system. For example the time period may be reduced if therecirculation rate is high, and local changes in concentration (e.g.,due to side reactions or gas leaks) may quickly be measured since thetime constants may be small.

Turning now to FIG. 2 , it shows an embodiment 300 of a field hydrationsystem 310 configured to couple to an external water supply 390. Solidlines in FIG. 2 indicate passages in the field hydration system, such asthe supply line 314, for conveying water. Intervening components locatedatop the solid lines illustrate one or more components arranged alongthe respective passages. The components may filter the water, transmitsignals to one or more controllers (including controller 88) indicatinga condition of the water (e.g., a conductivity, flow rate, and thelike), and the controller may send signals to the components forregulating flow to various passages located within the field hydrationsystem 310. The external water supply 390 is located outside of thefield hydration system 310 and is configured to deliver water to andreceive water from field hydration system 310 during hydration of aredox flow battery system fluidly coupled to the field hydration system310 at an end-use location. The hydration of a redox flow battery systemby way of field hydration system 310 is described in greater detailbelow with respect to FIGS. 4A, 4B, and 4C. As described above, acontroller, such as controller 88 may send and receive signals to one ormore sensors, valves, pumps, and the like, of the field hydration system310. In one example, field hydration system 310 may include its owndedicated controller is similar to the controller 88 of FIG. 1 . In thiscase, the dedicated controller and the controller 88 may send andreceive signals therebetween in order to coordinate hydration of theredox flow battery system. Furthermore, the dedicated controller and/orcontroller 88 may comprise executable instructions stored on memorythereon that enable the controllers to adjust various sensors andactuators described below in the field hydration system 310 and theredox flow battery system 10 in order to hydrate the redox flow batterysystem. Additionally or alternatively, one or more of the actionsdescribed herein may be performed manually by an operator.

The field hydration system 310 may be a portable system, and may bedelivered disassembled as its component parts to an end-use location ofthe redox flow battery system where the field hydration system can beassembled. In other examples, the field hydration system 310 may bedeployed in an assembled or partially assembled form to the end-uselocation where redox flow battery installation is desired. For example,the end-use location may include a customer's facility where energystorage provided by the redox flow battery system is to be utilized. Assuch, following delivery and installation of the redox flow batterysystem 10 at the end-use location, including fixedly coupling the redoxflow battery system to a surface (thereby fixing a position thereat),the field hydration system 310 may be assembled and fluidly coupled tothe redox flow battery system 10. As described above with reference toFIG. 1 , the field hydration system 310 may be fluidly coupled to theredox flow battery system 10 by way of one or more inlets and outlets toand from the negative and positive electrolyte chambers 50 and 52. Inthe example of FIG. 1 , the negative and positive electrolyte chambers50 and 52 are included within an integrated multi-chamber storage tank110. In other example redox flow battery systems, the negative andpositive electrolyte chambers 50 and 52 may respectively be included inseparate electrolyte storage tanks. The field hydration system 310comprises one or more components configured to prepare (e.g., hydrate)electrolytes for both positive and negative terminals of a redox flowbattery, as will be described in greater detail below. In the example ofFIG. 2 , field hydration system includes a water supply pump 312 forsupplying water from a supply source 392, filtration system 320, andbypass and diverter valves 336 and 340 for directing water to drain andto the electrolyte chambers, respectively.

The electrolyte preparation may include determining a desiredelectrolyte chemical composition, which may include determining astartup concentration of the electrolytes at each of the positive andnegative electrolyte chambers. The electrolytes may include one or moreof salts and acids, as described previously. The startup concentrationmay be based on one or more of composition of the electrolytes, thecomposition of the electrolyte chambers, the specific battery chemistry,and power output of the redox flow battery.

The field hydration system 310 comprises a water supply pump 312 fluidlycoupled to receive water from a water supply 392 of the external system390. In one example the water supply 392 may comprise a municipal watersupply or a treated water supply such as a deionized water or distilledwater supply. The water supply pump 312 is fluidly coupled to the watersupply 392 via a supply line 314. The supply line 314 may be a rigidpipe, flexible hose, and/or conduit configured to direct water from thewater supply 392 to the water supply pump 312. The supply line 314 maybe flexible, and or rigid, or both. In some embodiments, additionally oralternatively, the supply line 314 may comprise one or more bends toaccommodate a flow path for coupling the field hydration system 310 tothe water supply 392. A water intake control valve 316 may be positionedin the supply line 316 between the water supply 392 and the water supplypump 312 for adjusting water flow to the water supply pump 312. In oneexample, the water intake control valve 316 is an electronic valveelectrically coupled to one or more controllers (such as controller 88)and configured to actuate through a range of positions between fullyclosed and fully open. For example, the water intake control valve 316may move to a more closed position, where less water is admitted intothe supply line 314 than in a more open position. It will be appreciatedthat the water intake control valve 316 may be mechanical and/orpneumatic without departing from the scope of the present disclosure.

The water supply pump 312 may be electrically, hydraulically,electrically, and/or fuel powered. The water supply pump 312 isconfigured to direct water throughout one or more passages locateddownstream of the water supply pump 312 relative to a direction of waterflow. The water supply pump 312 draws water from the water supply 392,where the water flows through the supply line 314 and is directed by thewater supply pump 312 to a filtration system 320. The filtration system320 is downstream of the water supply pump 312 relative to a directionof water flow. The filtration system 320 may include one or more arraysor banks of filters arranged in parallel. Having a plurality of banksarranged in parallel may allow for a higher capacity of waterfiltration, and may enable continued filtration of water when a filtercapacity has been reached and while one or more filters are replaced.Each of the banks may comprise one or more filters configured to removecontaminants from the supply water. In the example hydration system ofFIG. 2 , a first bank of filters comprises a first filter 322, a secondfilter 324, and a third filter 326, corresponding to a three-stagefiltration. Likewise, a second bank of filters comprises a first filter322, a second filter 324, and a third filter 326, corresponding to athree-stage filtration. The first filters 322A and 322B may besubstantially identical to one another in size, shape, and composition.The first filters 322A and 322B may be deionizing or charcoal filters.

The second filters 324A and 324B and the third filters 326A and 326B maybe substantially identical in size, shape, and composition. The secondfilters 324A and 324B and third filters 326A and 326B may be deionizingor charcoal filters. In one example, the first filters 322A and 322B aredeionizing filters and the second filters 324A, 324B, and third filters326A, 326B are charcoal filters. Additionally or alternatively, one ormore of the filters may be a combination filter having both deionizingand charcoal elements. The filters may be configured to remove one ormore of salts, particulates, and other impurities, such that the waterexiting the filtration system 320 may have a conductivity less than athreshold conductivity. As such, water flowing downstream of thefiltration system 320 may consist essentially of H₂O, in one example.

The supply line 314 delivers water into the filtration system 320, wherethe supply line 314 bifurcates into a first filter passage 328A and asecond filter passage 328B. First filter 322A, second filter 324A, andthird filter 326A (e.g., the first filter set) are arranged along thefirst filter passage 328A. First filter 322B, second filter 324B, andthird filter 326B (e.g., the second filter set) are arranged along thesecond filter passage 328B. In one example, the first 328A and second328B filter passages are separated to increase a water flow rate throughthe filtration system 320. Filtered water from the first filter passage328 and the second filter passage 328 combine in a single feed line 332before flowing to a sensor.

One or more sensors 334 are arranged in the feed line 332 directlydownstream of the filtration system 320. In one example, the sensor 334includes a conductivity sensor 334. The conductivity sensor 334 isconfigured to measure a conductivity of the filtered water flowingthrough the feed line 332 toward a bypass valve 336 and a diverter valve340 fluidly coupled downstream from the bypass valve. In the example ofFIG. 2 , bypass valve 336 and diverter valves 340 are 3-way valves. Thismay be accomplished by monitoring a salt concentration in the waterdownstream of the filtration system 320. In one example, operation of adiverter valve 340 and/or a bypass valve 336 may be adjusted based onfeedback from the conductivity sensor. For example, if the conductivitysensor measures a filtered water sample having a conductivity greaterthan a threshold conductivity, then the controller (e.g., controller 88of FIG. 1 ) may signal to an actuator of bypass valve 336 to direct flowaway from diverter valve 340 to the drain 394. The thresholdconductivity may refer to a conductivity above which degradation of theredox flow battery system may occur or a coulombic efficiency of theflow battery system may be less than desired. For example, hydrating theredox flow battery system with water having a conductivity greater thanthe threshold conductivity may interfere with ion transport across theseparator, lower mass transfer and diffusion of metal ions to and fromthe battery cell electrodes, degrade pH control, induce premature chargecapacity loss, and the like. In this way, water having a higherconductivity may be delivered from the feed line 332 to the drain 394 ofthe external system 390 is fluidly coupled to the bypass line 338,thereby reducing a risk of degradation of the redox flow battery system.

In contrast, if the conductivity measured at sensor 334 is less than thethreshold conductivity, then the controller may position bypass valve336 to direct water flow towards diverter valve 340. Depending on aposition of diverter valve 340, filtered water may then be directed toflow towards the first electrolyte chamber 350 or the second electrolytechamber 360 of a redox flow battery system. In one example, the firstelectrolyte chamber 350 and the second electrolyte chamber 360 maycorrespond to the negative electrolyte chamber 50 and the positiveelectrolyte chamber 52, respectively, of an integrated multi-chamberstorage tank 110. In this way field hydration system 310 may be fluidlycoupled to the redox flow battery system 10. In other examples, thefirst electrolyte chamber 350 or the second electrolyte chamber 360 maycorrespond to negative and positive electrolyte chambers, eachpositioned in separate electrolyte storage tanks. Furthermore, the firstelectrolyte chamber may alternately represent a positive electrolytechamber and the second electrolyte chamber may represent a negativeelectrolyte chamber. By fluidly coupling the field hydration system tothe redox flow battery system 10, the negative and positive electrolytesolutions may be prepared in-situ and at the end-use location away fromthe battery manufacturing facility from a dry redox flow battery systemincluding dry electrolyte and free of water and wet electrolyte. Theflow rate of filtered water to first and second electrolyte chambers 350and 360 may be regulated by water supply pump 312.

As described above with reference to electrolyte chambers 50 and 52, thefirst electrolyte chamber and the second electrolyte chambers 350 and360 may each include one or more level sensors electrically coupled tothe controller 88. For example, first electrolyte chamber 350 maycomprise a first level sensor system 370 including a first level sensor372, a second level sensor 374, and a third level sensor 376. The first372, second 374, and third 376 level sensors maybe be vertically stackedabove one another, with the third sensor 376 being positioned higherthan the second level sensor 374 and the second sensor being positionedthan the first level sensor 372. In this way, the sensors may detectthree distinct fluid levels in the first electrolyte chamber 350, whichcan aid in facilitating a staged filling process thereof. In anotherconfiguration, first level sensor system 370 may include a pressure-typelevel sensor capable of measuring the fluid level in the firstelectrolyte chamber 350 based on a hydraulic pressure therein. A secondlevel sensor system 380 for the second electrolyte chamber 360 mayinclude first, second, and third level sensors 382, 384, and 386,respectively. The second level sensor system 380 may be configuredsimilarly to the first level sensor system 370, as previously described.

The second level sensor system 380 is substantially identical to thefirst level sensor system 370 in function, wherein both systems utilizethe sensors located therein for monitoring a fill-level of the tanks. Asan example, the first level sensor system 370 may monitor a stage-wisefilling the first electrolyte chamber 350 to lower, intermediate, andupper threshold volumes via the first 372, second 374, and third 376sensors, respectively. Likewise, the second level sensor system 380 maymonitor a stage-wise filling the second electrolyte chamber 360 tolower, intermediate, and upper threshold volumes via the first 382,second 384, and third 386 sensors, respectively. A location of sensorsin the first electrolyte chamber 350 and the second electrolyte chamber360 may thus be positioned to correspond to the lower, intermediate, andupper threshold volumes of both first and second electrolyte chambers350 and 360, respectively. The lower, intermediate, and upper thresholdvolumes of both first and second electrolyte chambers 350 and 360 may bethe same or disparate.

In some examples, additionally or alternatively, the field hydrationsystem 310 may be configured to drain one or more of the first 350 andsecond 360 electrolyte chambers. As such, a water level of one or moreof the first 350 and second 360 electrolyte chambers may decrease. Oncea sufficient amount of water is removed from the tanks, the tanks may besuitable for transportation to location different than the currentlocation. In some examples the liquid electrolyte may be completelydrained from the redox flow battery system, and a first and secondamount of dry electrolyte precursor may be added to the first and secondelectrolyte chambers. In one example, draining of liquid electrolytefrom the first and second electrolyte chambers may be conducted bydirecting electrolyte therefrom through diverter valve 340 and bypassvalve 336 to the drain 394. As previously described, the first andsecond amounts may correspond to a desired concentration of first andsecond electrolytes in the first and second electrolyte chambers duringan operating mode, In this way, electrolytes are shipped dry in theredox flow battery system from a first in-use location to a secondin-use location, where the electrolytes are hydrated in response to ademand to use the redox flow battery system. However, in response to ademand to move the redox flow battery system from the second location toa third in-use location, the electrolytes may be drained of water and/orliquid electrolyte and transported to the third location. In response toa demand to use the redox flow battery system, the electrolytes arehydrated similarly to the hydration at the second location.

Turning now to FIG. 3 , it shows a high-level flow chart depicting amethod 400 for hydrating a redox flow battery system with the fieldhydration system 310. Instructions for carrying out method 400 and therest of the methods included herein may be executed by a controller(e.g., controller 88) based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theredox flow battery system 10 and the field hydration system 310 such asthe sensors described above with reference to FIGS. 1 and 2 . Thecontroller may employ actuators of the redox flow battery system and/orfield hydration system of FIG. 2 to adjust operation thereof, accordingto the methods described below.

The method 400 begins at 402, where the method includes loadingchemicals (e.g., dry electrolyte precursors) into the first 350 andsecond 360 electrolyte chambers of FIG. 2 . As described above, in somecases, the dry electrolyte precursors may be pre-loaded prior todelivery to the end-use site. In other cases, the dry electrolyteprecursors may be shipped in appropriate storage vessels such as drumsor sacks, and loaded into the first and second electrolyte chambers atthe end-use location. In some cases, the electrolyte precursors may bein completely anhydrous form. In some cases, the precursors may be incrystal form. In some cases, the precursors may be in concentratedforms. In any case, the pre-hydrated redox flow battery system,including the first and second electrolyte chambers 350 and 360,consists essentially of a dry system, free of water and wet electrolyte.In the case of an IFB, the dry chemicals may include one or more ofFeCl₂, FeCl₃, FeSO₄, Fe₂(SO₄)₃, and the like. An amount of dry chemicalsloaded into each of the chambers may be based on a desired electrolytecomposition for each of the first and second electrolyte chambers. Thechemicals are loaded into the tanks and/or chambers dry and free ofwater and/or other liquid solvents. This ensures the chemicals arestored in the tanks and/or chambers in a dry state.

At 404, the method includes transporting the redox flow battery system,including the first and second electrolyte chambers 350 and 360, and thefield hydration system 310 to the end-use site. Transporting may includeshipping by truck, rail, ship, or other mode of transportation. Asdescribed above, in the dry state, the redox flow battery system, andthe field hydration system may be considered as portable systems.Furthermore, the field hydration system 310 may be disassembled into itscomponent parts to facilitate transport. Also at 404, the redox flowbattery system may be installed at the end-use location, fixing aposition thereof. Furthermore, the field hydration system may beassembled, installed, and fluidly coupled to the redox flow batterysystem. At 406, the method includes connecting a water supply pump 312of the field hydration system 310 to a water supply source 392 at theend-use location. In the example of FIG. 2 , the water supply pump 312is coupled to a water source 392 via the supply line 314. At 408, themethod includes hydration of the redox flow battery system. This mayinclude activating the water supply pump 312 and flowing water throughthe various hoses, pipes, filters, sensors, and valves of the fieldhydration system. Hydration of the redox flow battery system isdescribed in greater detail with respect to FIGS. 4A, 4B and 4C. At 410,following hydration of the redox flow battery system, the redox flowbattery system may begin operation as described with reference to FIG. 1. The redox flow battery system may begin operation, including chargingof the redox flow battery system, in response to decoupling the fieldhydration system 310 therefrom. After beginning operation of the redoxflow battery system, the field hydration system 310 may be disassembled,portably relocated, assembled and recoupled to the same or another redoxflow battery system for commissioning and hydrating the redox flowbattery system with the field hydration system and/or draining the redoxflow battery system. In this way the field hydration system togetherwith a redox flow battery system may convert the redox flow batterysystem to a self-draining rehydratable redox flow battery system.

Turning now to FIGS. 4A, 4B, and 4C, they show a method 500 forhydrating the dry electrolytes in the first and second electrolytechambers 350 and 360. Specifically, the method 500 further describeshydration of a dry redox flow battery system (step 408 of method 400 ofFIG. 3 ).

The method 500 begins at 502, where the method includes opening thewater intake control valve 316. In one example, the water intake controlvalve is moved to a fully open position to allow water from the watersupply to flow to the water supply pump 312 via the supply line. At 504,the method may include activating the water supply pump 312, whichconveys water flow through the field hydration system 310 to the firstand second electrolyte chambers 350 and 360. At 506, the method mayinclude flowing water through one or more filters of a filtration system320 to remove impurities, and to lower the supply water conductivity.

At 508, the method includes determining if a water conductivity is lessthan a threshold conductivity. The conductivity may be measured by oneor more conductivity sensors. If the water conductivity is not less thanthe threshold, one or more filters of the filtration system 320 may beexhausted. Thus method 500 may proceed from 508 to 510, where the bypasscontrol valve 336 may be positioned to direct water flow to the drain394, thereby bypassing the redox flow battery system. The waterconductivity may be continuously monitored by the controller viaconductivity sensor 334 throughout the method 500. Thus, at any pointduring hydration of the redox flow battery system may be stopped orpaused by positioning bypass control valve 336 to direct the supplywater flow to the drain during a condition where the conductivity of thesupply water is greater than the threshold conductivity.

For the case where the supply water conductivity is greater than thethreshold conductivity, method 500 may proceed to 512 from 510, wherethe method includes deactivating the water supply pump 312, therebystopping the supply of water from the water source external to the fieldhydration system. For example, water intake control valve 316 may beadjusted to the fully closed position, thereby preventing water fromflowing from the water source 392 to the supply line 314 of FIG. 2 .Next, at 514, in response to the supply water conductivity being greaterthan the threshold conductivity, the method may include signalingdegradation of one or more filters of the field hydration system.Signaling degradation may include sending an audio and/or visual signalto the operator. In the example of FIG. 2 , each of the filters isindicated degraded due to the conductivity sensor being locationdownstream of a junction where filtered water from the two banks offilters merge in the feed line. However, it will be appreciated thateach bank may comprise its own conductivity sensor, such that one bankmay be flagged as degraded and the other bank may not. Additionally oralternatively, a conductivity sensor may be located directly downstreamof each individual filter. In this way, each filter of the filter systemmay be individually diagnosed after water flows therethrough.

Returning to 508, if the water conductivity is less than the thresholdconductivity, then hydration of the dry electrolyte precursors in thefirst electrolyte chamber may be initiated, including stage-wise fillingand heating thereof. The method may proceed to 516 from 508, where themethod includes positioning the bypass valve 336 and the diverter valve340 to direct the flow of filtered water to the first electrolytechamber 350. As such, water from the filtration system 320 flows throughthe feed line 332, through the first electrolyte chamber passage 352,and into the first electrolyte chamber 350. In this way, hydration ofthe dry electrolyte precursors in the first electrolyte chamber 350 isinitiated. However, chemicals in the second electrolyte chamber and/orsecond chamber are free of water and remain dry. It will be appreciatedthat in alternative embodiments, water may flow to the secondelectrolyte chamber before flowing to the first electrolyte chamberwithout departing from the scope of the present disclosure.

At 518, the method may include determining if a first electrolytechamber volume is greater than a first threshold volume (e.g., a firstelectrolyte chamber lower threshold volume). Determining if the firstelectrolyte chamber volume is greater than the first threshold volumemay include determining if a fluid level in the first electrolytechamber 350 has reached the level of a first level sensor 372.Additionally or alternatively, a hydraulic pressure of the fluid in thefirst electrolyte chamber may reach a first threshold pressure, whichcorresponds to the first threshold volume. The first threshold volumemay correspond to a first dilution volume of the electrolyte in thefirst electrolyte chamber. After the fluid volume reaches the firstthreshold volume, enough dissolution of the dry electrolyte precursormay occur so that circulation and mixing of the fluid in the firstelectrolyte chamber can be started. In one example, the first thresholdvolume may include up to 20% of the volume of the first electrolytechamber. If the first electrolyte chamber volume is not greater than thefirst threshold volume, then the method may proceed from 518 to 520 tocontinue flowing water to the first electrolyte chamber withoutactivating the first electrolyte chamber heater and without activatingthe first electrolyte recirculation pump.

If the first electrolyte chamber volume is greater than or equal to thefirst threshold volume, then the method may proceed from 518 to 522,where the method includes activating or increasing power supplied to afirst electrolyte chamber heater in order to raise a temperature of thefluid in the first electrolyte chamber to a first threshold temperature.By increasing a temperature of the first electrolyte chamber solution,dissolution of the dry electrolyte precursors in the first electrolytechamber may occur more rapidly. As such, the first threshold temperaturemay be predetermined based on the solubility of the dry electrolyteprecursors; as the solubility increases, the first threshold temperaturemay decrease, and vice versa. Furthermore, at temperatures lower thanthe first threshold temperature dissolution may be incomplete orprecipitation may occur, which decreases homogeneity and may increasethe time consumed by the hydration process, thereby increasing operationcosts. In one example, the first threshold temperature may be between45-65° C.

At 524, the method may include activating an electrolyte recirculationpump fluidly connected to the first electrolyte chamber to recirculatethe fluid in the first electrolyte chamber to aid in more homogeneousmixing and heating of the electrolyte fluid and to accelerate saltdissolution. In one example, the electrolyte recirculation pump mayrefer to an electrolyte pump 30 or 32 fluidly connected to the firstelectrolyte chamber. In this way, fluid from the first electrolytechamber may be pumped via the electrolyte recirculation pump in arecirculation loop and returned to the first electrolyte chamber.Accordingly, during hydration of the redox flow battery system, a bypassvalve (not shown in FIG. 1 ), fluidly coupled between the electrolyterecirculation pump discharge and the first electrolyte chamber may bepositioned to divert fluid from the pump directly back to the firstelectrolyte chamber, bypassing the redox flow battery cells 18 of thepower module.

At 526, the method may include determining if the first electrolytechamber fluid volume is greater than the second threshold volume (e.g.,an intermediate threshold volume) greater than the first thresholdvolume. The second threshold volume may correspond to level indicated bya second level sensor (e.g., second level sensor 374) of the firstelectrolyte chamber. Additionally or alternatively, a hydraulic pressureof the fluid in the second electrolyte chamber may be equal to a secondthreshold pressure, which corresponds to an intermediate thresholdvolume of the first electrolyte chamber, between the lower and upperthreshold volumes.

If the first electrolyte chamber volume is not greater than or equal tothe second threshold volume, then the method may proceed from 526 to 528to continue flowing water to the first electrolyte chamber with theheater activated. The method continues to monitor a water level of thefirst electrolyte chamber. If the first electrolyte chamber volume isgreater than or equal to the second threshold volume, then stage-wisefilling of the first electrolyte chamber is paused, and the methodproceeds to 530 from 526 to shut-off flow of filtered water from thefiltration system 320 to the second electrolyte chamber 360.Additionally, the first electrolyte recirculation pump is switched offat 532. Although filling and recirculation of the first electrolytechamber is paused, heating of the first electrolyte chamber ismaintained at 534 of 4B. In one example, the fluid temperature of thefirst electrolyte chamber is maintained at the first thresholdtemperature. By maintaining the fluid temperature of the firstelectrolyte chamber at the first threshold temperature, a risk ofprecipitation in the first electrolyte chamber may be reduced.

Next, hydration of the dry electrolyte precursors in the secondelectrolyte chamber is initiated, including stage-wise filling andheating thereof. Hydration of the dry electrolyte precursors in thesecond electrolyte chamber is initiated, including stage-wise fillingand heating thereof, may proceed by way of steps 536 through 553,analogously to steps 516 through 534 for the first electrolyte chamber.In this way, hydration and stage-wise filling and heating of both thefirst and second electrolyte chambers may be started. In the case of anintegrated multi-chamber storage tank, stage-wise filling and heating ofthe first and second electrolyte chambers may facilitate maintaining apressure difference between the first and second electrolyte chambersless than a threshold pressure difference. Stage-wise filling andheating of the first and second electrolyte chambers may further allowfor faster heating and dissolution of the electrolyte since smallervolumes of fluid can be heated and used for dry electrolyte dissolution.

In some embodiments where only one of the first and second electrolytechambers comprises a heater, both chambers receive a similar amount ofwater and the chambers are fluidly coupled to heat solutions of each ofthe respective chambers. The amount of water may be greater than firstthreshold volume and less than the third threshold volume. In someexamples, the amount of water may be substantially equal to the thirdthreshold volume.

Next, at 554, the method includes initiating a first timer. In oneexample, the first timer tracks a duration of a hold time, the hold timebeing initiated in response to fluid in the first and second electrolytechambers reach the second and fourth threshold volumes, respectively.During the hold time, fluid in the first and second electrolyte chambersremain heated to the first and second electrolyte temperatures. Holdingthe heated fluid in the first and second electrolyte chambers may allowfor dissolution of the dry electrolyte precursors loaded to the firstand second electrolyte chamber, and for the solutions to equilibrate.Owing to the change in volume due to dissolution, the volume of fluid inthe first and second electrolyte chambers may increase during the holdtime even though water supply pump 312 is off and additional filteredwater is not supplied.

At 556, the method may include determining if the first timer is greaterthan a threshold time, indicating that the hold time has elapsed. Thethreshold time may correspond to an empirically predetermined hold timethat helps to ensure that electrolytes fluid in the first and secondelectrolyte chambers are thoroughly heated and mixed and equilibrated.In one example, the threshold time may be 60 minutes or more. If thefirst timer is not greater than the threshold time, then the method mayproceed to 558 from 556 where the method may continue the hold timewithout supplying water to the first and second electrolyte chambers.The method may continue to monitor a duration of the time delay via thefirst timer.

If the first timer is greater than the threshold time, then the methodmay proceed to 560 from 556, where the method may include determining ifthe first electrolyte chamber fluid volume is greater than a fifththreshold volume, the fifth threshold volume being larger than thesecond threshold volume. The fifth threshold volume may correspond tolevel indicated by a third level sensor 376 of the first electrolytechamber. Additionally or alternatively, a hydraulic pressure of thefluid in the first electrolyte chamber may be equal to a third thresholdpressure, which corresponds to a higher threshold volume of the firstelectrolyte chamber, greater than the lower and intermediate thresholdvolumes. If the first electrolyte chamber volume is not greater than thefifth threshold volume, then the method may proceed to 562 from 560,where the method may activate the water supply pump 312 supplying waterthrough the filtration system 320. As described above, the waterconductivity of the supply water as measured by the conductivity sensor334 may be continuously monitored by the controller throughout method500. Thus, at any time during execution of method 500, the flow ofsupply water may bypass to the drain 394 in response to the measuredwater conductivity being greater than the threshold conductivity bypositioning the bypass valve 336 to the drain 394.

Next, at 564, the method 500 may include positioning the bypass valve336 and the diverter valve 340 to direct the filtered water into thefirst electrolyte chamber 350. Following 564, method 500 returns back to560. Once the fluid volume in the first electrolyte chamber 350 reachesthe fifth threshold volume, at 570 the controller may switch off thewater supply pump and position the diverter valve 340 to stop flow offiltered water to the first electrolyte chamber, while continuing tomaintain the first electrolyte chamber at the first thresholdtemperature. In this way, stage-wise filling and hydration of theelectrolyte within the first electrolyte chamber is achieved.

Following 570, the method may proceed to 572 where the method mayinclude determining if the second electrolyte chamber fluid volume isgreater than a sixth threshold volume, the sixth threshold volume beinglarger than the fourth threshold volume. The sixth threshold volume maycorrespond to level indicated by a third level sensor 386 of the secondelectrolyte chamber. Additionally or alternatively, a hydraulic pressureof the fluid in the second electrolyte chamber may be equal to a thirdthreshold pressure, which corresponds to a higher threshold volume ofthe second electrolyte chamber, greater than the lower and intermediatethreshold volumes. If the first electrolyte chamber volume is notgreater than the sixth threshold volume, then the method may proceed to574 from 572, where the method may activate the water supply pump 312supplying water through the filtration system 320. As described above,the water conductivity of the supply water as measured by theconductivity sensor 334 may be continuously monitored by the controllerthroughout method 500. Thus, at any time during execution of method 500,the flow of supply water may bypass to the drain 394 in response to themeasured water conductivity being greater than the thresholdconductivity by positioning the bypass valve 336 to the drain 394.

Next, at 576, the method 500 may include positioning the bypass valve336 and the diverter valve 340 to direct the filtered water into thesecond electrolyte chamber 360. Following 576, method 500 returns backto 572. Once the fluid volume in the second electrolyte chamber 350reaches the sixth threshold volume, at 582 the controller may switch offthe water supply pump 312 and position the diverter valve 340 to stopflow of filtered water to the first electrolyte chamber, whilecontinuing to maintain the first electrolyte chamber at the firstthreshold temperature. In this way, stage-wise filling and hydration ofthe electrolyte within the second electrolyte chamber is achieved.Following 582, the method may proceed to method 300 after step 410, andends.

Once stage-wise filling and hydration of both first and secondelectrolyte chambers is achieved, the redox electrolyte system may beoperated, including supplying power to an external load duringdischarging, receiving power during a charging mode, and operating in anidle mode during which no charging or discharging of the redox flowbattery cells occurs.

In this way, a hydration procedure for a redox flow battery includestransporting dry electrolytes stored in tanks and hydrating theelectrolytes via a water source at a desired location. The electrolytesare hydrated via a field hydration system configured to filter waterfrom the water source and deliver a desired amount of water to each ofthe tanks comprising electrolytes. The technical effect of transportingthe electrolytes dry and mixing the electrolytes at the desired locationis to decrease a shipping cost and complexity of the redox flow batterysystem, while increasing flexibility in startup and operation logisticsof the redox flow battery system.

Thus, a method of operating a redox flow battery system, the redox flowbattery system including first and second electrolyte chambers fluidlycoupled to a redox flow battery cell, includes during a first condition,including when the redox flow battery system is in a dry state withoutwater and liquid solvents, adding first and second amounts of dryelectrolyte precursor to the first and second electrolyte chambers,respectively, the first and second amounts corresponding to a desiredconcentration of first and second electrolytes in the first and secondelectrolyte chambers during an operating mode, including when the redoxflow battery system is being charged or discharged, fluidly coupling theredox flow battery system to a field hydration system, the fieldhydration system including a water supply pump fluidly coupled to awater source, and supplying water from the field hydration system to theredox flow battery system, wherein the redox flow battery system wouldremain in the dry state without the water from the field hydrationsystem. A first example of the method includes during a secondcondition, including when the redox flow battery system is in a wetstate with greater than a threshold amount of water therein, directingthe water to the first electrolyte chamber, and in response to a firstelectrolyte chamber liquid level reaching a first threshold level,raising a temperature of the first electrolyte chamber to a firstthreshold temperature, the first threshold temperature being greaterthan an ambient temperature. A second example of the method optionallyincludes the first example and further includes stopping the supply ofwater from the field hydration system to the redox flow battery systemin response to a conductivity of the supplied water increasing above athreshold conductivity. A third example of the method optionallyincludes one or more of the first and second examples and furtherincludes during the second condition, in response to the firstelectrolyte chamber liquid level reaching the first threshold level,recirculating the first electrolyte chamber liquid level with acirculation pump fluidly coupled to the first electrolyte chamber. Afourth example of the method optionally includes one or more of thefirst through third examples and further includes during the secondcondition, in response to the first electrolyte chamber liquid levelreaching a second threshold level, stopping the supply of water to thefirst electrolyte chamber and deactivating the circulation pump, whereinthe second threshold level is higher than the first threshold level. Afifth example of the method optionally includes one or more of the firstthrough fourth examples and further includes during the secondcondition, in response to the first electrolyte chamber liquid levelreaching the second threshold level, directing water to the secondelectrolyte chamber, the second electrolyte chamber being in the drystate prior to the first electrolyte chamber liquid level reaching thesecond threshold level. A sixth example of the method optionallyincludes one or more of the first through fifth examples and furtherincludes wherein the redox flow battery system comprises a multi-chamberstorage tank, the multi-chamber storage tank including the first andsecond electrolyte chambers, and the supply of water to the firstelectrolyte chamber is stopped until a second electrolyte chamber liquidlevel reaches the second threshold level. A seventh example of themethod optionally includes one or more of the first through sixthexamples and further includes maintaining a pressure difference betweenthe first and second electrolyte chambers less than a threshold pressuredifference. An eighth example of the method optionally includes one ormore of the first through seventh examples and further includes duringthe second condition, in response to a second electrolyte chamber liquidlevel reaching a third threshold level, raising a temperature of thesecond electrolyte chamber to a second threshold temperature the secondthreshold temperature being greater than the ambient temperature. Aninth example of the method optionally includes one or more of the firstthrough eighth examples and further includes during the secondcondition, in response to the second electrolyte chamber liquid levelreaching a fourth threshold level, stopping the supply of water to thesecond electrolyte chamber, wherein the fourth threshold level isgreater than the third threshold level. A tenth example of the methodoptionally includes one or more of the first through ninth examples andfurther includes during the second condition, in response to the secondelectrolyte chamber liquid level reaching the fourth threshold level,maintaining the first and second electrolyte chambers at the first andsecond threshold temperatures for a threshold duration. An eleventhexample of the method optionally includes one or more of the firstthrough tenth examples and further includes in response to the thresholdduration expiring, filling the first and second electrolyte chamberswith the water. A twelfth example of the method optionally includes oneor more of the first through eleventh examples and further includesduring the first condition, prior to coupling the redox flow batterysystem to the field hydration system, assembling the redox flow batterysystem and transporting the assembled redox flow battery system from abattery manufacturing facility to an end-use location different from thebattery manufacturing facility. A thirteenth example of the methodoptionally includes one or more of the first through twelfth examplesand further includes wherein the second condition further comprisesfluidly coupling the redox flow battery system to a field hydrationsystem at the end-use location.

Thus, a redox flow battery system includes a redox flow battery cellfluidly coupled to positive and negative electrolyte chambers, dryelectrolytes located in the positive and negative electrolyte chamberswith less than a threshold amount of solvents, a field hydration systemdetachably coupled to a water source arranged externally to the redoxflow battery, and a controller, including executable instructions storedthereon to, activate a water supply pump of the field hydration systemconfigured to flow water from the water source to the positive andnegative electrolyte chambers. A first example of the redox flow batterysystem includes wherein the field hydration system comprises a divertervalve and a bypass valve, wherein the executable instructions furthercomprise opening the bypass valve and closing the diverter valve inresponse to a water conductivity being greater than a thresholdconductivity, where flowing water through the open bypass valve includesflowing water out of the field hydration system and away from thepositive and negative electrolyte chambers. A second example of theredox flow battery system optionally includes the first example andfurther includes a conductivity sensor positioned downstream of afiltration system, the conductivity sensor and the filtration systemfluidly interposed between the water supply pump and the diverter valve,wherein the filtration system comprises two or more filters divided intotwo or more filter banks. A third example of the redox flow batterysystem optionally includes one or more of the first and second examplesand further includes wherein the executable instructions furthercomprise instructions opening the diverter valve and closing the bypassvalve in response to a water conductivity measured by the conductivitysensor being less than the threshold conductivity, and wherein flowingwater through the open diverter valve includes flowing water to one ormore of the positive and negative electrolyte chambers. A fourth exampleof the redox flow battery system optionally includes one or more of thefirst through third examples and further includes wherein the executableinstructions further comprise charging the redox flow battery system inresponse to decoupling the field hydration system from the redox flowbattery.

Thus, a redox flow battery system may include first and secondelectrolyte chambers fluidly coupled to a redox flow battery cell, and acontroller with executable instructions stored in non-transitory memorythereon to, during a first condition, including when the redox flowbattery system is in a dry state without water and liquid solvents, addfirst and second amounts of dry electrolyte precursor to the first andsecond electrolyte chambers, respectively, the first and second amountscorresponding to a desired concentration of first and secondelectrolytes in the first and second electrolyte chambers during anoperating mode, including when the redox flow battery system is beingcharged or discharged, fluidly couple the redox flow battery system to afield hydration system, the field hydration system including a watersupply pump fluidly coupled to a water source, and supply water from thefield hydration system to the redox flow battery system, wherein theredox flow battery system would remain in the dry state without thewater from the field hydration system.

Note that the example control and estimation routines included hereincan be used with various battery configurations. The control methods androutines disclosed herein may be stored as executable instructions innon-transitory memory and may be carried out by the control systemincluding the controller in combination with the various sensors,actuators, and other battery hardware. The specific routines describedherein may represent one or more of any number of processing strategiessuch as event-driven, interrupt-driven, multi-tasking, multi-threading,and the like. As such, various actions, operations, and/or functionsillustrated may be performed in the sequence illustrated, in parallel,or in some cases omitted. Likewise, the order of processing is notnecessarily required to achieve the features and advantages of theexample embodiments described herein, but is provided for ease ofillustration and description. One or more of the illustrated actions,operations and/or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described actions,operations and/or functions may graphically represent code to beprogrammed into non-transitory memory of the computer readable storagemedium in the engine control system, where the described actions arecarried out by executing the instructions in a system including thevarious battery hardware components in combination with the electroniccontroller.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method of operating a redox flow battery system, the redox flowbattery system including first and second electrolyte chambers fluidlycoupled to a redox flow battery cell, the method comprising: during afirst condition as determined by a controller, including when the redoxflow battery system is in a dry state without water and liquid solvents,adding first and second amounts of dry electrolyte precursor to thefirst and second electrolyte chambers, respectively, the first andsecond amounts corresponding to a desired concentration of first andsecond electrolytes in the first and second electrolyte chambers duringan operating mode, including when the redox flow battery system is beingcharged or discharged, fluidly coupling the redox flow battery system toa field hydration system, the field hydration system detachably fluidlycoupled to the first and second electrolyte chambers of the redox flowbattery system and including a water supply pump detachably fluidlycoupled to a water source, supplying water from the field hydrationsystem to the redox flow battery system, wherein the redox flow batterysystem would remain in the dry state without the water from the fieldhydration system, stopping, via the controller of the redox flow batterysystem controlling one or more actuators, a supply of water from thefield hydration system to the redox flow battery system in response to aconductivity of the supplied water increasing above a thresholdconductivity as determined by the controller, the conductivitydetermined using signals received from a conductivity sensor of thefield hydration system, and operating the redox flow battery system,wherein operating the redox flow battery system includes both chargingby applying a charging current and discharging via oxidation andreduction of the first and second electrolytes.
 2. The method of claim1, further comprising, during a second condition as determined by thecontroller, including when the redox flow battery system is in a wetstate with greater than a threshold amount of water therein, directing,via the controller, the water to the first electrolyte chamber, and inresponse to a first electrolyte chamber liquid level reaching a firstthreshold level as determined by the controller and before operating theredox flow battery system, raising a temperature of the firstelectrolyte chamber to a first threshold temperature via the controller,the first threshold temperature being greater than an ambienttemperature.
 3. The method of claim 1, wherein the field hydrationsystem is detachably fluidly coupleable to the redox flow battery systemby way of one or more inlets and outlets to and from the first andsecond electrolyte chambers, each of the first and second electrolytechambers comprising negative and positive electrolyte chambers,respectively, wherein the field hydration system comprises one or morecomponents configured to prepare electrolytes for both positive andnegative terminals of the redox flow battery system, the one or morecomponents including the water supply pump for supplying water from asupply source, a filtration system, and bypass and diverter valves fordirecting water to drain and to the negative and positive electrolytechambers, wherein the redox flow battery system is configured to bedry-assembled at a battery manufacturing facility different from anend-use location without filling and hydrating the redox flow batterysystem before delivery of the redox flow battery system to the end-uselocation, wherein the end-use location corresponds to a location wherethe redox flow battery system is to be installed and utilized as a fixedlocation, non-portable, on-site energy storage, and wherein the fieldhydration system permits automated and controlled hydration of the redoxflow battery system once in the end-use location.
 4. The method of claim2, further comprising, during the second condition as determined by thecontroller, in response to the first electrolyte chamber liquid levelreaching the first threshold level as determined by the controller,recirculating, via the controller controlling the one or more actuators,the first electrolyte with a circulation pump fluidly coupled to thefirst electrolyte chamber.
 5. The method of claim 1, further comprising,during the first condition, prior to coupling the redox flow batterysystem to the field hydration system, assembling the redox flow batterysystem and transporting the assembled redox flow battery system from abattery manufacturing facility to an end-use location different from thebattery manufacturing facility.
 6. The method of claim 5, whereinfluidly coupling the redox flow battery system to the field hydrationsystem is performed at the end-use location.
 7. A redox flow batterysystem, comprising: a field hydration system that is separate from theredox flow battery system and detachably fluidly coupleable to positiveand negative electrolyte chambers of the redox flow battery system, thefield hydration system comprising a water supply pump, a diverter valve,a bypass valve, and a conductivity sensor; a redox flow battery cellfluidly coupled to the positive and negative electrolyte chambers; dryelectrolytes located in the positive and negative electrolyte chamberswith less than a threshold amount of solvents; the field hydrationsystem detachably fluidly coupleable to a water source arrangedexternally to the redox flow battery; and a controller, includingexecutable instructions stored thereon to, activate the water supplypump of the field hydration system configured to flow water from thewater source to the positive and negative electrolyte chambers; open thebypass valve and close the diverter valve in response to a waterconductivity being greater than a threshold conductivity to flow waterthrough the open bypass valve, where flowing water through the openbypass valve includes flowing water out of the field hydration systemand away from the positive and negative electrolyte chambers, the waterconductivity determined by the controller based on signals received fromthe conductivity sensor; and charge by applied current and discharge theredox flow battery cell during operation.
 8. A redox flow batterysystem, including first and second electrolyte chambers fluidly coupledto a redox flow battery cell, and a controller with executableinstructions stored in non-transitory memory thereon to: during a firstcondition as determined by the controller, including when the redox flowbattery system is in a dry state without water and liquid solvents, addfirst and second amounts of dry electrolyte precursor to the first andsecond electrolyte chambers, respectively, the first and second amountscorresponding to a desired concentration of first and secondelectrolytes in the first and second electrolyte chambers during anoperating mode, including when the redox flow battery system is beingcharged by applied current or discharged, fluidly couple the redox flowbattery system to a field hydration system using one or more actuatorscontrolled by the controller, the field hydration system detachablyfluidly coupled to the first and second electrolyte chambers of theredox flow battery system and including a water supply pump detachablyfluidly coupled to a water source, supply water from the field hydrationsystem to the redox flow battery system, wherein the redox flow batterysystem would remain in the dry state without the water from the fieldhydration system, stop, via the controller of the redox flow batterysystem controlling one or more actuators, the supply of water from thefield hydration system to the redox flow battery system in response to aconductivity of the supplied water increasing above a thresholdconductivity as determined by the controller, the conductivitydetermined using signals received from a conductivity sensor of thefield hydration system, and operate the redox flow battery system in atleast one operating mode in response to decoupling the field hydrationsystem from the redox flow battery system.